1. Field of the Invention
The present invention relates to methods and apparatus for controlling electrically powered steering systems in motor vehicles. More particularly, embodiments described herein are directed to controlling and/or adjusting a torque value involved in steering a vehicle equipped with electrically powered steering.
2. Description of the Related Art
Conventional motor vehicles typically include a steering system having a steering wheel that controls one or more ground wheels in order to control the direction of travel of the vehicle. Rotation of the steering wheel by a driver causes the one or more ground wheels to turn or realign, which, when the vehicle is in motion, causes the vehicle to change direction. These vehicles typically include some form of power-assist system which reduces the torque required to rotate the steering wheel while providing the mechanical force required to turn the one or more ground wheels. The power-assist systems include hydraulic systems and more recently, electrically powered systems, commonly referred to as electric power steering (EPS) systems.
These systems facilitate a reduction in the torque value required to rotate the steering wheel. Conventional hydraulic steering systems require about 25-30 foot·pounds (ft·lbs) of torque to rotate the steering wheel. EPS systems may be slightly more or less, depending on the type of vehicle and the factory torque value setting provided by the original equipment manufacturer (OEM). EPS systems also typically include steering effort adjustments based solely on the speed of travel of the vehicle.
While the EPS systems significantly lower the effort involved in steering the vehicle, the torque level used to turn the steering wheel is not low enough for all drivers. For example, individuals with a spinal cord injury or other debilitating disability, as well as some elderly individuals, may not have the physical strength to rotate the steering wheel at these conventional levels. These individuals often need additional reduced effort steering that is less than the OEM torque levels deliver in order to safely operate the vehicle.
Various methods for reducing steering effort in hydraulic systems are available. However, EPS systems are not easily modified due to the presence of electronic components on vehicles equipped with EPS systems, such as an electronic control unit (ECU), a controller area network (CAN), and the like, which typically perform diagnostics on the vehicle systems, including the EPS system. Thus, modification of EPS systems to reduce steering effort may cause the EPS system to malfunction and/or shut down.
Therefore, a need exists for methods and apparatus for modifying an EPS system to adjust the steering effort to a desired torque value that provides enhanced low effort steering of the vehicle.